1. Field of the Invention
This invention relates to an apparatus for making a racket frame, more particularly to an apparatus for preforming a main body of a racket frame from a softened fiber reinforced thermoplastic resin composite tube.
2. Description of the Related Art
Fiber reinforced composite materials have gradually replaced metal alloys as the primary material in the manufacture of exercise equipments due to their relatively light weight and ability to be cast to form a wide variety of exercise equipments. Presently, majority of the racket frames that are available in the market are made of a fiber reinforced thermosetting resin composite material which is formed of unidirectional prepreg. There are also racket frames which are made of a thermoplastic resin composite material that is formed by injection forming, braiding or filament winding. However, a thermoplastic resin composite racket frame formed of unidirectional prepreg is not disclosed because the raw thermoplastic resin composite material is relatively hard such that the production thereof is difficult.
Accordingly, in co-pending U.S. patent application Ser. No. 08/079,756, the applicant disclosed a method for manufacturing a fiber reinforced thermoplastic resin composite racket frame. In the co-pending application, a thermoplastic resin composite material formed of unidirectional prepreg is used. The process steps includes: (a) cutting a thermoplastic resin composite fabric formed of unidirectional prepreg into sheets of predetermined size and fiber orientation angle; (b) preforming a tube including: stacking the sheets of thermoplastic resin composite fabric; heating the stacked sheets to a predetermined softening temperature of the stacked sheets; wrapping the heated sheets around a mandrel to form the tube; and withdrawing the tube from the mandrel; and (c) shaping the tube into a racket frame by placing the tube inside a mold.